Rat Phosphoenolpyruvate Carboxykinase Research Articles

Retraction Note: The impact of vitamin A supplementation on thyroid function and insulin sensitivity: implication of deiodinases and phosphoenolpyruvate carboxykinase in male Wistar rats

Retraction Note: The impact of vitamin A supplementation on thyroid function and insulin sensitivity: implication of deiodinases and phosphoenolpyruvate carboxykinase in male Wistar rats

RETRACTED ARTICLE: The impact of vitamin A supplementation on thyroid function and insulin sensitivity: implication of deiodinases and phosphoenolpyruvate carboxykinase in male Wistar rats

PurposeVitamin A is an essential nutrient with vital biological functions. The present study investigated the effect of different doses of vitamin A palmitate at different time intervals on thyroid hormones and glycemic markers.MethodsMale rats were administrated vitamin A palmitate at different doses (0, 0.7, 1.5, 3, 6, and 12 mg/kg, oral) and samples were collected at different time intervals of 2, 4, and 6 weeks. The levels of vitamin A, thyroid hormones (T3, T4, and TSH), deiodinases (Dio1 and Dio3), glycemic markers (blood insulin and fasting glucose levels, HOMA IR and HOMA β), retinol-binding protein 4 (RBP4) and the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) were measured.ResultsThe findings demonstrated that long-term supplementation with high doses of vitamin A palmitate resulted in hypothyroidism (lower T3 and T4 levels and elevated TSH levels) as well as upregulation of Dio1 and Dio3 expression levels. This effect was associated with elevated glucose and insulin levels, enhanced HOMA IR, and decreased HOMA B index. In addition, prolonged vitamin A supplementation significantly increased RBP4 levels that upregulated the expression of PEPCK.ConclusionHigh doses of vitamin A supplementation increased the risk of hypothyroidism, modulated insulin sensitivity, and over a long period, increased the incidence of type 2 diabetes mellitus associated with oxidative stress and hepatitis.

Melatonin stimulates transcription of the rat phosphoenolpyruvate carboxykinase gene in hepatic cells.

Melatonin plays physiological roles in various critical processes, including circadian rhythms, oxidative stress defenses, anti-inflammation responses, and immunity; however, the current understanding of the role of melatonin in hepatic glucose metabolism is limited. In this study, we examined whether melatonin affects gene expression of the key gluconeogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK). We found that melatonin treatment increased PEPCK mRNA levels in rat highly differentiated hepatoma (H4IIE) cells and primary cultured hepatocytes. In addition, we found that melatonin induction was synergistically enhanced by dexamethasone, whereas it was dominantly inhibited by insulin. We also report that the effect of melatonin was blocked by inhibitors of mitogen-activated protein kinase/extracellular signal-regulated protein kinase (MAPK/ERK), RNA polymerase II, and protein synthesis. Furthermore, the phosphorylated (active) forms of ERK1 and ERK2 (ERK1/2) increased 15min after melatonin treatment. We performed luciferase reporter assays to show that melatonin specifically stimulated promoter activity of the PEPCK gene. Additional reporter analysis using 5'-deleted constructs revealed that the regulatory regions responsive to melatonin mapped to two nucleotide regions, one between -467 and -398 nucleotides and the other between -128 and +69 nucleotides, of the rat PEPCK gene. Thus, we conclude that melatonin induces PEPCK gene expression via the ERK1/2 pathway at the transcriptional level, and that induction requires denovo protein synthesis.

Induction of the SHARP-2 mRNA level by insulin is mediated by multiple signaling pathways.

The rat enhancer of split- and hairy-related protein-2 (SHARP-2) is an insulin-inducible transcription factor which represses transcription of the rat phosphoenolpyruvate carboxykinase gene. In this study, a regulatory mechanism of the SHARP-2 mRNA level by insulin was analyzed. Insulin rapidly induced the level of SHARP-2 mRNA. This induction was blocked by inhibitors for phosphoinositide 3-kinase (PI 3-K), protein kinase C (PKC), and mammalian target of rapamycin (mTOR), actinomycin D, and cycloheximide. Whereas an adenovirus infection expressing a dominant negative form of atypical PKC lambda (aPKCλ) blocked the insulin-induction of the SHARP-2 mRNA level, insulin rapidly activated the mTOR. Insulin did not enhance transcriptional activity from a 3.7kb upstream region of the rat SHARP-2 gene. Thus, we conclude that insulin induces the expression of the rat SHARP-2 gene at the transcription level via both a PI 3-K/aPKCλ- and a PI 3-K/mTOR- pathways and that protein synthesis is required for this induction.

Dynamic Behavior of Rat Phosphoenolpyruvate Carboxykinase Inhibitors: New Mechanism for Enzyme Inhibition

As an enzyme acting at the junction of gluconeogenic pathway, phosphoenolpyruvate carboxykinase (PEPCK) controls substrate flow from Krebs cycle toward glucose production. Therefore, it would be advantageous to design effective inhibitors to inactivate PEPCK in diabetes mellitus and other abnormalities caused by insulin resistance. Such inhibitors may compensate the metabolic consequences of ex-activity of PEPCK at these conditions. Understanding the mechanism by which inhibitors exert their effect on enzyme activity is of great interest for designing stronger inhibitors. In the present work, molecular dynamic simulations were used to study enzyme-inhibitor interactions. Our results indicate that inhibitors of PEPCK with their short chains interact with enzyme active site through non-covalent interactions of electrostatic and hydrogen bond nature. The data also show that inhibitors neither reach a stable state in their binding site nor make static complex with the enzyme active site. Instead, they interact with functional groups of active site residues in a dynamic fashion. In this way, oxalate and sulfoacetate carrying two negative groups of higher charge density and optimum spacing from each other, show more dynamic behavior (lower stability in their binding site) and more inhibitory effects than other inhibitors used (phosphonoformate, phosphoglycolate and 3-phosphonopropionate).

Insulinotropic effect of cinnamaldehyde on transcriptional regulation of pyruvate kinase, phosphoenolpyruvate carboxykinase, and GLUT4 translocation in experimental diabetic rats

Diabetes mellitus is a chronic metabolic disorder affecting about 6% of population worldwide with its complications and is rapidly reaching epidemic scale. Cinnamomum zeylanicum is widely used in alternative system of medicine for treatment of diabetes. In the present study, we have performed bioassay guided fractionation of chloroform extract of C. zeylaniucm and identified cinnamaldehyde (CND) as an active principle against diabetes. In continuation to it, a detailed study was undertaken to elucidate its mode of antidiabetic action in STZ induced diabetic rats. Oral administration of CND (20 mg/kg bw) to diabetic rats for 2 months showed significant improvement ( p < 0.001) in muscle and hepatic glycogen content. In vitro incubation of pancreatic islets with CND enhanced the insulin release compared to glibenclamide. The insulinotropic effect of CND was found to increase the glucose uptake through glucose transporter (GLUT4) translocation in peripheral tissues. The treatment also showed a significant improvement in altered enzyme activities of pyruvate kinase (PK) and phosphoenolpyruvate carboxykinase (PEPCK) and their mRNA expression levels. Furthermore, the median lethal dose (LD 50) of CND could not be obtained even at 20 times (0.4 g/kg bw) of its effective dose. With the high margin of safety of CND, it can be developed as a potential therapeutic candidate for the treatment of diabetes.

Glucocorticoids and phenobarbital induce murine CYP2B genes by independent mechanisms

Background: Genes for CYP of the 2B subfamily (CYP2B genes) have long been known to be inducible in murine liver by phenobarbital and phenobarbital-like inducers. More recently, it has become clear that glucocorticoids can also induce these genes by a mechanism independent of that of phenobarbital-like inducers. Objective: To summarize the evidence for the existence of two distinct molecular mechanisms for induction of murine CYP2B genes and to analyze the wider implications of this situation for inducible xenobiotic metabolism. Methods: The mechanism of action of phenobarbital-like inducers of murine CYP2B genes is first briefly summarized. The role of glucocorticoids in the induction of various proteins, particularly rat phosphoenolpyruvate carboxykinase, where transcriptional activation is achieved via a glucocorticoid response unit, is also discussed. Finally, recent results are presented on glucocorticoid induction of murine CYP2B genes, including evidence for the presence of a functional glucocorticoid response unit in the rat CYP2B2 gene and for the role of constitutive androstane receptor as an accessory factor in this response. Results/conclusion: Murine CYP2B genes are seen to respond to two distinct regulatory mechanisms, but much remains to be learned concerning the interactions between these two regulatory loops, as well as the details of glucocorticoid induction.

New Evidence on Hypoglycemic Effect of Quinolinic Acid in Diabetic Rats

In the present study, the effects of administrating 4 mM and 300 mg kg(-1) b.wt. of quinolinic acid were studied, in vitro and in vivo, respectively, to evaluate its inhibitory activity on phosphoenolpyruvate carboxykinase in diabetic rats. The results of in vitro studies have clearly indicated the inhibitory effect of quinolinic acid on enzyme activity. The hill plot showed the binding stoichiometry of quinolinic acid per enzyme to be 4:1. The in vivo studies showed that intra peritoneal injection of 300 mg kg(-1) b.wt. initiates reduction of blood glucose level in 1 h after injection, restoring the blood glucose to its normal level at 2 h post injection and keeping it constant for at least further 4 h. Based on present results we concluded that quinolinic acid and hence its precursor tryptophan having induced obvious hypoglycemic effects in normal and diabetic rats at high enough concentrations, they are worthy of further study and research for their hyperglycemic effect in other diabetic animal models.

Plasma Glucose Lowering Effect of the Wild Satureja khuzestanica Jamzad Essential Oil in Diabetic Rats: Role of Decreased Gluconeogenesis

This study was to evaluate the effect of the wild SKEO on activities and genes expression of hepatic Glycogen Phosphorylase (GP) and phosphoenolpyruvate carboxykinase (PEPCK) in normal and diabetic rats. The wild SKEO was orally administered at different doses (50 and 100 mg/kg/day) to normal as well as diabetic rats for 21 days. The levels of mRNA were determined using the quantitative real-time RT-PCR technique. The plasma glucose concentrations of diabetic rats receiving SKEO (100 mg kg(-1)) compared with diabetic control were significantly decreased. Hepatic GP activity and its mRNA levels of diabetic rats treated with SKEO moderately increased. The activity of hepatic PEPCK and its mRNA levels were significantly decreased in normal rats treated with SKEO (100 mg kg(-1)). The enhancement of PEPCK activity and its mRNA levels of diabetic treated rats with SEKO (100 mg kg(-1)) was significantly decreased compared with diabetic control. In conclusion, an excessive inhibition of PEPCK in liver of diabetic rats treated with the wild SKEO may contribute to the plasma glucose lowering action of SKEO that seems to be in relation with antioxidant properties of SKEO.

Protein-tyrosine Phosphatase 1B Deficiency Reduces Insulin Resistance and the Diabetic Phenotype in Mice with Polygenic Insulin Resistance

Mice heterozygous for insulin receptor (IR) and IR substrate (IRS)-1 deficiency provide a model of polygenic type 2 diabetes in which early-onset, genetically programmed insulin resistance leads to diabetes. Protein-tyrosine phosphatase 1B (PTP1B) dephosphorylates tyrosine residues in IR and possibly IRS proteins, thereby inhibiting insulin signaling. Mice lacking PTP1B are lean and have increased insulin sensitivity. To determine whether PTP1B can modify polygenic insulin resistance, we crossed PTP1B-/- mice with mice with a double heterozygous deficiency of IR and IRS-1 alleles (DHet). DHet mice weighed slightly less than wild-type mice and exhibited severe insulin resistance and hyperglycemia, with approximately 35% of DHet males developing diabetes by 9-10 weeks of age. Body weight in DHet mice with PTP1B deficiency was similar to that in DHet mice. However, absence of PTP1B in DHet mice markedly improved glucose tolerance and insulin sensitivity at 10-11 weeks of age and reduced the incidence of diabetes and hyperplastic pancreatic islets at 6 months of age. Insulin-stimulated phosphorylation of IR, IRS proteins, Akt/protein kinase B, glycogen synthase kinase 3beta, and p70(S6K) was impaired in DHet mouse muscle and liver and was differentially improved by PTP1B deficiency. In addition, increased phosphoenolpyruvate carboxykinase expression in DHet mouse liver was reversed by PTP1B deficiency. In summary, PTP1B deficiency reduces insulin resistance and hyperglycemia without altering body weight in a model of polygenic type 2 diabetes. Thus, even in the setting of high genetic risk for diabetes, reducing PTP1B is partially protective, further demonstrating its attractiveness as a target for prevention and treatment of type 2 diabetes.

Farnesoid X Receptor Agonist Reduces Serum Asymmetric Dimethylarginine Levels through Hepatic Dimethylarginine Dimethylaminohydrolase-1 Gene Regulation

The farnesoid X receptor (FXR, NR1H4) is a bile acid-responsive nuclear receptor that plays critical roles in the transcriptional regulation genes involved in cholesterol, bile acid, triglyceride, and carbohydrate metabolism. By microarray analysis of hepatic genes from female Zucker diabetic fatty (ZDF) rats treated with the FXR agonist GW4064, we have identified dimethylarginine dimethylaminohydrolase-1 (DDAH1) as an FXR target gene. DDAH1 is a key catabolic enzyme of asymmetric dimethylarginine (ADMA), a major endogenous nitric-oxide synthase inhibitor. Sequence analysis of the DDAH1 gene reveals the presence of an FXR response element (FXRE) located 90 kb downstream of the transcription initiation site and within the first intron. Functional analysis of the putative FXRE demonstrated GW4064 dose-dependent transcriptional activation from the element, and we have demonstrated that the FXRE sequence binds the FXR-RXR heterodimer. In vivo administration of GW4064 to female ZDF rats promoted a dose-dependent and >6-fold increase in hepatic DDAH1 gene expression. The level of serum ADMA was reduced concomitantly. These findings provide a mechanism by which FXR may increase endothelium-derived nitric oxide levels through modulation of serum ADMA levels via direct regulation of hepatic DDAH1 gene expression. Thus, beneficial clinical outcomes of FXR agonist therapy may include prevention of atherosclerosis and improvement of the metabolic syndrome.

Merit of physical exercise to reverse the higher gene expression of hepatic phosphoenolpyruvate carboxykinase in obese Zucker rats

Effects of endurance training on the phosphoenolpyruvate carboxykinase (PEPCK), a rate-limiting enzyme of gluconeogenesis, were studied in the obese Zucker rats. We used a moderate exercise program consisting of treadmill running at 20 m/min and 0-degree gradient for 1 h/day, 7 days/week, for 8 weeks. At the end of the experimental period, insulin action on glucose disposal rate was measured using the glucose–insulin index, the product of the areas under the curve of glucose and insulin during the intraperitoneal glucose tolerance test. Furthermore, changes of hepatic PEPCK gene expression were detected using reverse transcriptase polymerase chain reaction to assay the mRNA level and Western blot analysis to detect the protein level. Different to sedentary obese rats, an elevation in the value of glucose–insulin index from the exercised obese rats declined, indicating the marked effect of regular moderate exercise on the improvement of insulin sensitivity in this insulin resistant animal model. Moreover, the diabetes-related elevation in mRNA level and protein content of hepatic PEPCK were observed in non-exercise obese groups but they were markedly reduced by exercise training. In addition, chronic exercise training enhanced the insulin sensitivity of lean Zucker rats, since the value of glucose–insulin index was lower than that of untrained lean groups. Also, the hepatic PEPCK gene expressions both the mRNA and protein levels were reduced in exercised lean Zucker rats as compared with their sedentary littermates. These results suggest that modulation of hepatic PEPCK gene expression by chronic exercise training might be related to the enhancement of insulin sensitivity. Thus, endurance exercise training could aid in the prevention and/or treatment of individuals with insulin resistance.

3′-Untranslated Region of Phosphoenolpyruvate Carboxykinase mRNA Contains Multiple Instability Elements That Bind AUF1

Phosphoenolpyruvate carboxykinase (PEPCK) is regulated solely by alterations in gene expression that involve changes in rates of PEPCK mRNA transcription and degradation. A tetracycline-responsive promoter system was used to quantify the half-life of various chimeric beta-globin-PEPCK (betaG-PCK) mRNAs in LLC-PK -F(+) cells. The control betaG mRNA was extremely stable (t(1/2) = 5 days). However, betaG-PCK-1 mRNA, which contains the entire 3'-UTR of the PEPCK mRNA, was degraded with a half-life of 1.2 h. RNase H treatment indicated that rapid deadenylation occurred concomitant with degradation of the betaG-PCK-1 mRNA. Previous studies indicate that PCK-7, a 50-nucleotide segment at the 3'-end of the 3'-UTR, binds an unidentified protein that may contribute to the rapid decay of the PEPCK mRNA. However, the chimeric betaG-PCK-7 mRNA has a half-life of 17 h. Inclusion of the adjacent PCK-6 segment, a 23-bp AU-rich region, produced the betaG-PCK-6/7 mRNA, which has a half-life of 3.6 h. The betaG-PCK-3 mRNA that contains the 3'-half of 3'-UTR was degraded with the same half-life. Surprisingly, the betaG-PCK-2 mRNA, containing the 5'-end of the 3'-UTR, was also degraded rapidly (t((1/2)) = 5.4 h). RNA gel shift analyses established that AUF1 (hnRNP D) binds to the PCK-7, PCK-6, and PCK-2 segments with high affinity and specificity. Mutational analysis indicated that AUF1 binds to a UUAUUUUAU sequence within PCK-6 and the stem-loop structure and adjacent CU-region of PCK-7. Thus, AUF1 binds to multiple destabilizing elements within the 3'-UTR that participate in the rapid turnover of the PEPCK mRNA.

Hepatocyte CYP2E1 Overexpression and Steatohepatitis Lead to Impaired Hepatic Insulin Signaling

Insulin resistance and increased cytochrome P450 2E1 (CYP2E1) expression are both associated with and mechanistically implicated in the development of nonalcoholic fatty liver disease. Although currently viewed as distinct factors, insulin resistance and CYP2E1 expression may be interrelated through the ability of CYP2E1-induced oxidant stress to impair hepatic insulin signaling. To test this possibility, the effects of in vitro and in vivo CYP2E1 overexpression on hepatocyte insulin signaling were examined. CYP2E1 overexpression in a hepatocyte cell line decreased tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and IRS-2 in response to insulin. CYP2E1 overexpression was also associated with increased inhibitory serine 307 and 636/639 IRS-1 phosphorylation. In parallel, the effects of insulin on Akt activation, glycogen synthase kinase 3, and FoxO1a phosphorylation, and glucose secretion were all significantly decreased in CYP2E1 overexpressing cells. This inhibition of insulin signaling by CYP2E1 overexpression was partially c-Jun N-terminal kinase dependent. In the methionine- and choline-deficient diet mouse model of steatohepatitis with CYP2E1 overexpression, insulin-induced IRS-1, IRS-2, and Akt phosphorylation were similarly decreased. These findings indicate that increased hepatocyte CYP2E1 expression and the presence of steatohepatitis result in the down-regulation of insulin signaling, potentially contributing to the insulin resistance associated with nonalcoholic fatty liver disease.

SHARP-2/Stra13/DEC1 as a potential repressor of phosphoenolpyruvate carboxykinase gene expression

The influence of the enhancer of split- and hairy-related protein-2 (SHARP-2) transcriptional repressor on the expression of rat phosphoenolpyruvate carboxykinase ( PEPCK) gene was examined. When H4IIE cells were treated with epigallocatechin gallate, a green tea constituent, an increase in SHARP-2 mRNA levels and a decrease in PEPCK mRNA levels were observed. The adenovirus-mediated overexpression of SHARP-2 in H4IIE cells and primary cultured rat hepatocytes led to a decrease in the levels of PEPCK mRNA. Finally, when a SHARP-2 expression plasmid was transiently transfected with various reporter plasmids into MH 1C 1 cells, the promoter activity of a PEPCK reporter plasmid was specifically decreased. Based on these findings, we conclude that SHARP-2 is a potential repressor of PEPCK gene expression.

Hyperglycemia associated with increased hepatic glycogen phosphorylase and phosphoenolpyruvate carboxykinase in rats following subchronic exposure to malathion

We examined the effects of subchronic exposure to malathion, an organophosphorous (OP) insecticide, on plasma glucose and hepatic enzymes of glycogenolysis and gluconeogenesis in rats in vivo. Malathion was administered orally at doses of 100, 200 and 400 ppm for 4 weeks. At the end of the specified treatment (18 h fasting after the last dose of malathion), the liver was removed. The activities of glycogen phosphorylase (GP) and phosphoenolpyruvate carboxykinase (PEPCK) were analyzed in the homogenate. Four weeks administration of malathion at doses of 100 ppm, 200 ppm, and 400 ppm increased plasma glucose concentrations by 25% ( P<0.01), 17% ( P<0.01), and 14% ( P<0.01) of control, respectively. Malathion also increased hepatic PEPCK activity by 25% (100 ppm, P<0.01), 16% (200 ppm, P<0.01), and 21% (400 ppm, P<0.01) of control, respectively. In addition, malathion increased hepatic GP by 22% (100 ppm, P<0.01), 41% (200 ppm, P<0.01), and 32% (400 ppm, P<0.01) of controls. We conclude that exposure of rats to malathion as a widely used OP in subchronic exposure, which resembles human exposure, may induce diabetes associated with stimulation of hepatic gluconeogenesis and glycogenolysis in favor of glucose release into the blood. The possible mechanisms including increased energy production to detoxification, depressed paraoxonase activity, and increased production of cyclic nucleotides are discussed.

Effects of overexpression of growth hormone on T cell activity in transgenic mice.

Growth hormone plays a key role in the maturation and maintenance of the immune response, however, the effects of chronic high circulating concentrations of the hormone on the immune system is poorly understood. Transgenic mice overexpressing bovine growth hormone (b-GH) gene, fused to the rat phosphoenolpyruvate carboxykinase promoter (PEPCK), with very high plasma concentration of heterologous b-GH and their littermate normal siblings were used. Spleen cellularity, percentages of total T lymphocytes, CD4+ and CD8+ cells, ratio of T cell subpopulations, mitogen-induced lymphocyte proliferation and natural killer (NK) cell activity were examined in male transgenic mice and normal littermate mice at 2 and 6 months of age. The number of splenic lymphocytes was greater in transgenic mice than in matched normal littermates at both ages. The NK cell activity was lower in transgenic mice than in the matched normal littermates at both ages, with the lowest values found in older mice. The b-GH transgenic mice had lower percentages of T cells at both ages, however, in young transgenic mice, the percentage of CD4+ cells was reduced while percentage of CD8+ cells was increased in comparison to normal controls. Both basal and mitogen-induced proliferation capacity of splenocytes were reduced in PEPCK-b-GH-25 mice as compared to normal littermates of both ages. Proliferative indexes in response to concanavalin A and phytohemagglutinin were markedly decreased in 6 month old PEPCK-b-GH-25 mice as compared to littermate controls or younger mice. These results indicate that overexpression of b-GH in mice is associated with decreased T cell function and that these abnormalities are age-dependent.

Phosphoenolpyruvate Carboxykinase Overexpression Selectively Attenuates Insulin Signaling and Hepatic Insulin Sensitivity in Transgenic Mice

The ability of insulin to suppress gluconeogenesis in type II diabetes mellitus is impaired; however, the cellular mechanisms for this insulin resistance remain poorly understood. To address this question, we generated transgenic (TG) mice overexpressing the phosphoenolpyruvate carboxykinase (PEPCK) gene under control of its own promoter. TG mice had increased basal hepatic glucose production (HGP), but normal levels of plasma free fatty acids (FFAs) and whole-body glucose disposal during a hyperinsulinemic-euglycemic clamp compared with wild-type controls. The steady-state levels of PEPCK and glucose-6-phosphatase mRNAs were elevated in livers of TG mice and were resistant to down-regulation by insulin. Conversely, GLUT2 and glucokinase mRNA levels were appropriately regulated by insulin, suggesting that insulin resistance is selective to gluconeogenic gene expression. Insulin-stimulated phosphorylation of the insulin receptor, insulin receptor substrate (IRS)-1, and associated phosphatidylinositol 3-kinase were normal in TG mice, whereas IRS-2 protein and phosphorylation were down-regulated compared with control mice. These results establish that a modest (2-fold) increase in PEPCK gene expression in vivo is sufficient to increase HGP without affecting FFA concentrations. Furthermore, these results demonstrate that PEPCK overexpression results in a metabolic pattern that increases glucose-6-phosphatase mRNA and results in a selective decrease in IRS-2 protein, decreased phosphatidylinositol 3-kinase activity, and reduced ability of insulin to suppress gluconeogenic gene expression. However, acute suppression of HGP and glycolytic gene expression remained intact, suggesting that FFA and/or IRS-1 signaling, in addition to reduced IRS-2, plays an important role in downstream insulin signal transduction pathways involved in control of gluconeogenesis and progression to type II diabetes mellitus.

Drug-induced acute interstitial nephritis

Drug-induced acute interstitial nephritis

Characterization of a kidney-specific pattern of chromatin structure in the rat phosphoenolpyruvate carboxykinase gene

The kidney-specific chromatin structure of the phosphoenolpyruvate carboxykinase (PEPCK) gene was examined and compared to that of the liver. Kidney nuclear extracts were found to lack a liver-enriched factor, pepA, that binds to HSS A, a distal enhancer of the PEPCK gene that may be involved in opening the chromatin domain of the PEPCK gene in the liver. To begin the characterization of the kidney-specific chromatin structure of the PEPCK gene, nuclease hypersensitive sites (HSS) were mapped by indirect end-labeling analysis in proximal tubules from control rats, proximal tubules from acidotic rats which express induced levels of PEPCK, and NRK52E cells, a rat kidney epithelial cell line which does not express the PEPCK gene. A subset of HSS, at −400/+1 over the proximal promoter and at +1900 within the coding region, correlate with kidney-specific PEPCK expression. Two other HSS, at −3.1 kb and +6.2 kb, are detected in kidney cells regardless of PEPCK expression. The HSS at −4800, −1240, and +4650, previously identified in PEPCK-expressing liver cells, were not observed in the kidney. As in the liver, the pattern of hypersensitivity in the kidney does not change by altering the rate of transcription.